1. Field of the Invention
Exemplary embodiments of the present invention relates to a probe and an antenna; and, more particularly, to a probe and antenna using a waveguide.
2. Description of Related Art
An antenna is a generic term of devices for transmitting or receiving electromagnetic waves. A probe in a wide sense refers to an antenna for receiving electromagnetic waves, and in a narrow sense refers to an electromagnetic wave receiver used for measuring electromagnetic fields.
Probes or antennas using waveguides have been known. A waveguide is a type of transmission lines for transmitting electromagnetic waves or electrical energy. A waveguide has a conductive cavity through which electromagnetic waves are transmitted. In general, since a waveguide has low ohmic loss and low dielectric loss, it is widely used in probes and antennas.
Meanwhile, in probes and antennas, multiple reflection is frequently problematic. The multiple reflection refers to a phenomenon in which an electromagnetic wave is several times reflected between two specific objects. The following description will be made with reference to an example which measures characteristics of an antenna by using a probe to measure an electromagnetic field around the antenna.
With regard to characteristics of the antenna, a space electromagnetically influenced by the antenna may be largely divided into a far field and a near field. The far field represents a space far away from the antenna by more than several times the wavelength of the electromagnetic wave used in the antenna, generally, more than three to five times. The near field represents a space far away from the antenna by less than several times the wavelength of the electromagnetic wave used in the antenna. It can be understood that the far field represents a space farther than a location where the electromagnetic field is completely formed from the antenna and thus it is isolated from the antenna. Also, it can be understood that the near field represents a space covering a location where the electromagnetic field is formed from the antenna.
Generally, an antenna transmits or receives electromagnetic waves by using an electromagnetic field formed in a far field. Therefore, characteristics of an antenna are usually measured in a far field. In some cases, however, characteristics of an antenna may be measured in a near field, and characteristics of an antenna in a far field may be calculated mathematically. Examples of such cases may include a case where a transmission loss is high because a measurement frequency is high, a case where an object to be measured is significantly large compared with the wavelength of an electromagnetic wave, and a case where far field measurement conditions are not met because of limitations in a measurement environment.
In such cases, a probe is disposed in a near field space, and characteristics of an antenna are measured. In those cases, an electromagnetic wave reception unit of the probe and a radiator of the antenna become very close to each other. Therefore, the multiple reflection of an electromagnetic wave may occur between the probe and the antenna. The probe may accurately measure characteristics of the antenna when it receives only electromagnetic waves radiated directly from the antenna. However, if characteristics of an antenna are measured in a near field, electromagnetic waves radiated from the antenna may be reflected one or more times at the probe or the antenna and then incident into the probe. Such a multiple-reflected electromagnetic wave serves as an error factor in measurement.
Furthermore, in a case where a frequency band of a signal to be measured is low, a wavelength of an electromagnetic wave is long and therefore a distance between a probe and an antenna must be large. Since characteristics of an antenna are usually measured inside a shield room or the like, there may be a limitation in increasing the distance between the probe and the antenna. In some cases, due to another limitation in a measurement environment, the distance between the probe and the antenna must be maintained to be narrow. In those cases, the distance between the probe and the antenna may be reduced by decreasing the multiple reflection of an electromagnetic wave.
Therefore, there is a need for methods which are capable of reducing the multiple reflection of electromagnetic waves in probes or antennas.